Anonymity and irreversibility are key values of BitCoin transactions. Merchants however might want to build reputation and customer might want to provide feedback. To add these features without touching on core values may I suggest you to consider introducing an additional "trust chain" as follows:

Assuming A buys from B a gadget using BitCoin whereby A only knows B's receiver address b. B as most merchants requires payment before delivery. A transfers funds to b and runs the risk until he receives the gadget. As the gadget arrives A is happy that b is a trustworthy address and might want to share this information with others by signing the transaction on a trust chain that is built similar to the money chain. B might also appreciate this since it gives him reputation for the next business. Note that neither A or B reveal more about their identity than available on the main Bitcoin chain.

B might be tempted to forge the trust chain to increase his reputation and generate transactions where he is the payer of BitCoin from other adresses then vote for himself. This however would be revealed if money chain is consulted, since he needs money for each transaction that will be reconcilable to a small number of sources if he were attempting to generate a good history in a short time frame.